1. Field of the Invention
This invention lies in the field of thermostable polymer systems which can be cross-linked by irradiation and which are adapted for microelectronic applications.
2. Prior Art
It is known that multi-layered wiring laminates can be produced by pressing onto one another thin layers of printed circuits which each contain an appropriate wiring image using adhesive foils between adjacent layers. The printed circuit layers and the adhesive foils form insulating layers between individual conductive paths. Following the formation of the multi-layered laminated circuit boards, the wiring connections and contact points between the individual layers are produced by means of bores and subsequent through-contacting of these bores.
In order to avoid crack formations in the adhesive contact layer and in the intermediate printed circuit layers, and delamination effects caused during soldering or in temperature stress changes, the process as described above has been improved upon by providing that both sides of a thin-layer printed circuit are provided with a copper layer, and each such copper layer is overcoated with a photo-resist coating. This photoresist coating, which can represent a negative or a positive image when exposed (imaged) by light while covered with a corresponding mask, is developed after imaging. The change effectd by light exposure is usually one of solubility and results in solvent discrimination between exposed and unexposed areas. Photo cross-linking and photoinitiated polymerization decrease solubility, whereas photomodification of functionality and photodegradation increase it. The remaining developed resin in regions in a developed residual layer serves as resist regions during a subsequent etching process for the copper. A desired conductive image is thus formed in areas to which an imaged and developed resist coating adheres when a negative resist coating is used and after the exposed copper has been removed by etching. These resin residues from an imaged and developed photo resist coating are subsequently removed either with organic solvents or mechanically, and then a next layer is applied.
In the case of image formation by means of irradiation, it is necessary to differentiate between a low energy radiation region (wavelength exceeding about 100 nm) and a high energy radiation region, for example, X-rays or electron rays. Naturally, the image resolution from an exposure to an imaging radiation source increases when radiation of a shorter wavelength is used. As disclosed in an article by A Ledwith in "IEEE Proceedings", Vol. 130, Part 1, No. 5, October 1983 on pages 245 to 251, the resolution limits are about 1 .mu.m for ultraviolet (UV) radiation and about 80 .ANG. for electron radiation.
Conductive path intervals (widths) of less than about 20 .mu.m are required for the construction of microelectronic components. Consequently, the material which is used must have a low dielectric constant. As disclosed in an article by A. J. Blodgett in "Spektrum der Wissenschaft", September, 1983, pages 94 to 106, the dielectric constant needs to have a value of less than about 3. It is disclosed in the same article that in the case of highly integrated components, during operation, a high thermal continuous stress (load) occurs which is approximately in the region of about 100.degree. C.
There is a need in the art for new and improved radiation-sensitive cross-linkable polymer systems thermostable which are adapted for microelectronic applications.